How did the Alliance systems contribute to World War 2?

Answer 1

The Alliance system allowed countries to make allies with other countries secretly. Therefore, a war which would have involved only a few countries involved the entire world because allies backed each other up in war. WW2 isn't a good example since Hitler would have probably run through all of Europe anyway, and eventually the US, to eradicate those he thought "impure". WW1 however is a great example because a war which would have been between Austria Hungry and Serbia ended up encompassing the world due to alliances.

Answer 2

Not much, since allies can usually find a way out of their undertakings if they want to. France had an alliance with Poland, but its similar obligations to Czechoslovakia hadn't counted for much the year before. Britain allied with Poland a week before the latter's invasion by Germany, but would have declared war anyway under its March guarantee. The alliance that counted was the one that didn't happen, between Britain, France and the USSR - the one thing that would have deterred German action: Poland considered the likely territorial price too high to pay.